Engine control procedures

Abstract

Procedure that includes: while a hybrid vehicle is driven by the torque of an electric motor (26), rotating an electrically operated intake compressor with an upstream closed intake throttle and an open EGR valve (152) until a piston temperature is above a limit value.

Description

Area

[0001] The present application relates to methods for controlling engine cranking power in a hybrid vehicle system. Background and Summary

[0002] Engines can be designed with direct fuel injectors that inject fuel directly into a combustion cylinder (direct injection) and / or with port fuel injectors that inject fuel into a cylinder's intake manifold (port fuel injection). Direct injection allows for greater fuel efficiency and higher power output, in addition to better utilizing the charge-cooling effect of the injected fuel.

[0003] DE 103 06 586 A1 discloses a method for preheating a specific area of ​​an internal combustion engine. An electrically operated intake compressor is rotated with an open EGR valve, and the process is terminated after a predetermined period. Two warm-up processes are described, which heat either the cylinder or the catalytic converter. When heating the cylinder, the EGR valve remains closed; when heating the catalytic converter, the EGR valve is open.

[0004] However, direct-injection engines can produce higher emissions of particulate matter (PM) (or soot) due to diffuse flame spread, where the fuel does not adequately mix with air prior to combustion. Because direct injection is inherently a relatively late fuel injection, there may be insufficient time for the injected fuel to mix with air in the cylinder. Under some operating conditions, the liquid fuel droplet may directly impinge on combustion surfaces such as the piston, head, and cylinder liner. Similarly, the injected fuel does not encounter turbulence as it flows through the valves. Consequently, pockets of vigorous combustion may occur, which can locally generate soot, thereby degrading exhaust emissions. Emissions may also be increased during cold-start engine operation.In particular, until the combustion chamber is fully warmed up, soot is generated due to poor fuel evaporation caused by the poor spray characteristics of the fuel injectors at low fuel rail pressure and / or fuel impinging on the cold metal surfaces of the combustion chamber.

[0005] Engine test data indicate that PM emissions can be reduced by increasing engine temperature. Thus, an electric engine heater may be included in some engine systems. For example, as shown by Vigild et al. in US 2012 / 0 291 762 A1, an intake heater is operated during DFSO conditions, where the engine fuel supply is disabled. By heating the air pumped to the engine cylinders, the engine can be heated sufficiently to reduce soot emissions.

[0006] However, the inventors have identified potential problems with such an approach. For example, sufficient heating may not be possible due to the limited time available before engine start. Likewise, due to the limited power available on the vehicle and the large engine mass, the available heating may be insufficient. As such, the power required for sufficient engine heating may be higher, resulting in poor fuel economy.

[0007] Some of the above problems may be addressed by taking advantage of various combinations of engine compression heating as well as compression stroke heating of individual cylinders. One example method includes, while driving a hybrid vehicle via electric motor torque, rotating an electrically actuated intake compressor with a closed intake throttle and an open EGR valve until a piston temperature is greater than a threshold. Another example method includes, while driving a hybrid vehicle via electric motor torque only, rotating an engine without fuel via electric motor torque at less than engine crank speed while operating an exhaust heater coupled to an exhaust catalyst and while maintaining an EGR valve open and an intake throttle closed to recirculate heated air charge through the engine.However, other combinations can be used in different heating modes. This allows cylinder heating to be increased before an engine is restarted.

[0008] For example, while a hybrid vehicle is operating in electric mode, prior to an imminent engine start and in response to cylinder piston temperatures not being sufficiently high, the engine may be slowly cranked, without fuel, via the hybrid vehicle's electric motor / generator to heat the engine cylinders. In one example, slow cranking may be initiated at least 2-3 minutes prior to an engine start. The engine may be slowly rotated at less than one engine crank speed, such as 10-30 rpm. During slow engine rotation, each cylinder may be sequentially taken through a cylinder compression stroke, where heat is transferred from the compressed air to the cylinder walls, head, and piston.Although the absolute amount of heat transferred to the engine may be small, the heat is transferred directly to a location where the heating enables a reduction in soot emissions when fuel is resumed. While the engine is rotating, an intake throttle may be held closed while an EGR valve is held open, so that the heated air charge is pumped in a loop, further enhancing cylinder heat transfer. Optionally, one or more of an electric intake heater and an electric exhaust catalyst heater may be operated simultaneously to further increase the temperature of the charge being passed through the engine cylinders. In addition to increasing the cylinder temperature, the slow engine rotation allows fuel rail pressure to be increased. Once cylinder temperatures are sufficiently high, e.g.When the piston temperature is higher than a threshold, and when conditions for restarting the engine are met, the engine can be rotated faster during cranking and the supply of fuel to the engine can be resumed.

[0009] In another example, while the hybrid vehicle is operating in an electric mode, an electric motor coupled to an electrically actuated compressor may be operated in response to the need for cylinder piston heating. During rotation of the compressor, heat is generated during the compression of air. While the compressor is rotating, cylinder valve timing may be adjusted to increase valve overlap and improve blow-by of the compressed air through the engine cylinders. This allows heat from the heated air charge to be transferred into the cylinders during blow-by. While the compressor is rotating, an intake throttle may be held closed while an EGR valve is held open, pumping the heated air charge in a loop, further improving cylinder heat transfer.Optionally, one or more of an electric intake heater and an electric exhaust catalyst heater may be operated simultaneously to further increase the temperature of the charge circulated through the engine cylinders. In some examples, a compressor return valve may be opened along with the rotation of the compressor so that the compressor energy can also be used to heat a downstream charge air cooler. Still further, while the compressor is rotating, the engine may also be rotated slowly, without fuel, so that the heated air can be evenly distributed to all engine cylinders. Once cylinder piston temperatures are sufficiently high, if conditions exist for an engine restart, the compressor rotation may be deactivated, the engine may be cranked, and fueling to the engine may resume.

[0010] In this way, by operating an electrically actuated intake compressor before an engine restart, the rotation of the compressor can be used to compress air charge, generating heat. By rotating the compressor with a compressor return valve in the open state, heat from the compressed air can be repulsed at a downstream charge air cooler. By simultaneously opening an EGR valve and closing an intake throttle, the heated air charge can be looped over the engine. In addition, heating of the air charge can be amplified through the use of an intake or exhaust heater. Additionally, or optionally, by slowly rotating the engine without fuel and using the torque of the electric motor, the pumped air can also be forced through one or more cylinders, warming the cylinders before an engine restart.Additionally, compression stroke heating can be used to heat the cylinders. By preheating the engine, particulate matter emissions from the engine can be reduced, especially during a cold start. Additionally, fuel pressure can be increased to an optimal starting level, improving the spray characteristics of the fuel injector during restart. Overall, cold start emissions can be improved.

[0011] It should be understood that the above summary is provided to provide, in a simplified form, a selection of concepts further described in the detailed description. It is in no way intended to identify key or essential features of the claimed subject matter, the scope of which is defined solely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that resolve any disadvantages noted above or elsewhere in this disclosure. Short description of the drawings Fig. 1 shows an exemplary embodiment of a hybrid vehicle system. Fig. 2 shows an exemplary design of a motor system. Fig. 3 shows an exemplary combustion chamber. Fig. 4 shows an exemplary method for compression heating of engine cylinders prior to engine start. Fig. Figure 5 shows an exemplary method for heating engine cylinders using heat generated during various combinations of engine rotation and compressor rotation. Fig. Figure 6 shows a table listing different modes of engine heating operation. Fig. Figure 7 illustrates an example map of cylinder heating during the compression stroke. Fig. Figure 8 illustrates an exemplary engine heating operation to reduce particulate matter emissions from a hybrid vehicle system. Detailed description

[0012] The following description relates to systems and methods for reducing particulate emissions from an engine, such as an engine system of the Fig. 2-3, which is coupled in a hybrid vehicle system, such as the plug-in hybrid electric vehicle of the Fig. 1. A controller can be designed to execute a routine, such as the exemplary routines of Fig. 4-5, to rotate the engine, without fuel, during vehicle operation using the torque of the electric motor, in order to thereby draw air from the compressed air in a compression stroke ( Fig. 7) to transfer the heat generated to heat the engine's combustion chambers while also increasing fuel pressure. Additionally, the controller can rotate an electrically operated compressor of the engine system to heat the engine using compressor energy. The controller can perform various combinations of compression heating as shown in the table of Fig. 6. An example engine heating operation is shown in Fig. 8. In this way, particulate emissions from the engine can be reduced, especially during cold starts.

[0013] Fig. 1 illustrates a hybrid propulsion system 100 for a vehicle. In the illustrated embodiment, the vehicle is a hybrid electric vehicle (HEV). The propulsion system 100 includes an engine system 5 with an internal combustion engine 10 having a plurality of cylinders 30. Fuel may be provided to each cylinder of the engine 10 from a fuel system (not shown) that includes one or more fuel reservoirs, one or more fuel pumps, and one or more fuel injectors 66. The fuel injectors 66 may be configured for direct injection, port injection, or a combination of both. A detailed description of an exemplary engine coupled in a hybrid propulsion system 100 is provided in Fig. 2 provided.

[0014] The engine 10 supplies power to a transmission 44 via a torque input shaft 18. In the illustrated example, the transmission 44 is a power-split transmission (or transaxle) that includes a planetary gear set 22 and one or more rotating gear elements. The transmission 44 further includes an electric generator 24 and an electric motor 26. The electric generator 24 and electric motor 26 may also be referred to as electric machines, as each operates as either a motor or a generator. Torque is output from the transmission 44 to drive drive wheels 52 of the vehicle via a power transfer gear 34, a torque output shaft 19, and a differential-axle assembly 36.

[0015] The generator 24 is drivingly connected to the electric motor 26 so that each of the electric generator 24 and the electric motor 26 can be operated using electrical energy from an electrical energy storage device, depicted here as a battery 54. In some embodiments, a power conversion device, such as an inverter, can be coupled between the battery and the motor to convert the DC output of the battery to an AC output for use by the motor. However, in other embodiments, the inverter can be configured in the electric motor.

[0016] The electric motor 26 can be operated in a regenerative mode, i.e., as a generator, to absorb energy from the vehicle's motion and / or the engine and convert the absorbed kinetic energy into a form of energy suitable for storage in a battery 54. Furthermore, the electric motor 26 can be operated as a motor or generator, as needed, to augment or absorb torque provided by the engine.

[0017] The planetary gear set 22 includes a ring gear 42, a sun gear 43, and a planetary carrier assembly 46. The ring gear and the sun gear may be coupled to each other via the carrier. A first input side of the planetary gear set 22 is coupled to the engine 10, while a second input side of the planetary gear set 22 is coupled to the generator 24. An output side of the planetary gear set is coupled to the drive wheels 52 of the vehicle via a power transmission gear 34 that includes one or more meshing gear elements 60-68. In one example, the meshing gear elements 60-68 may be stepped gears in which a carrier assembly 46 may distribute torque to the stepped gears. The gear elements 62, 64, and 66 are mounted on a countershaft 17, with gear element 64 meshing with an electric, motor-driven gear element 70.The electric motor 26 drives the gear member 70, which acts as a torque input for the countershaft gear. In this way, the planetary carrier 46 (and consequently the motor and generator) may be coupled to the vehicle wheels and the engine via one or more gear members. The hybrid propulsion system 100 may operate in various embodiments, including a full hybrid system, where the vehicle is powered solely by the motor and generator in cooperation, or solely by the electric motor, or in a combination. Alternatively, auxiliary or mild hybrid embodiments may be employed, where the engine is the primary source of torque and the electric motor selectively adds torque during specific conditions, such as during an acceleration event.

[0018] For example, the vehicle may be driven in a motor mode in which the engine 10 is operated as the primary source of torque for driving the wheels 52. During the motor mode, fuel may be supplied to the engine 10 from a fuel tank via the fuel injector 66 so that the fueled engine can rotate rapidly to provide torque for driving the vehicle. In particular, engine power is supplied to the ring gear of the planetary gear train. Simultaneously, the generator provides torque to the sun gear 43, thereby producing a reaction torque for the engine. Consequently, the torque is output from the planetary carrier to the gears 62, 64, 66 on the countershaft 17, which in turn supply power to the wheels 52.In addition, the engine may be operated to output more torque than is required for propulsion, in which case the additional energy is absorbed by the generator (in generation mode) to charge the battery 54 or to supply electrical energy for other vehicle loads.

[0019] In another example, the vehicle may be driven in an auxiliary mode in which the engine 10 is operated and used as the primary source of torque to drive the wheels 52, and in which the electric motor is used as an additional torque source to cooperate with and supplement the torque provided by the engine 10. During the auxiliary mode, as in the motor mode, fuel is supplied to the engine 10 to fuel the engine to rapidly spin and provide torque to the vehicle wheels.

[0020] In yet another example, the vehicle may be driven in an engine-off mode or an electric mode in which the battery-powered electric motor 26 is operated and used as the sole source of torque to drive the wheels 52. As such, during the electric mode, no fuel is injected into the engine 10, regardless of whether the engine is spinning rapidly or not, and the vehicle is propelled using only the torque of the electric motor alone. The electric mode may be used, for example, during braking, at low speeds, with low loads, when stopping at traffic lights, etc. In particular, the power of the electric motor is supplied to the gear member 70, which in turn drives the gear members on the countershaft 17, and thereafter drives the wheels 52.

[0021] The drive system 100 may further include a control system including a controller 12 configured to receive information from a plurality of sensors 16 (various examples of which are described herein) and send control signals to a plurality of actuators 81 (various examples of which are described herein). For example, the sensors 16 may include various pressure and temperature sensors, a fuel level sensor, various exhaust gas sensors, etc. The various actuators may include, for example, the transmission, the cylinder fuel injectors (not shown), an air intake throttle coupled to the engine intake manifold (not shown), etc. Additional sensors and actuators are described in the Fig. 2-3. The controller 12 may receive input data from the various sensors, process the input data, and trigger the actuators in response to the processed input data based on a command or code programmed therein corresponding to one or more routines. Exemplary control routines are described herein with reference to Fig. 4-5 described.

[0022] Direct-injected engines as such can generate a large amount of particulate matter (or soot), particularly during cold-start operations. This is largely due to the poor spray characteristics of the fuel injector at low fuel pressures during engine startup. In addition, soot is generated due to fuel impinging on the cold metal surfaces of the combustion chamber during startup. Soot generation can be substantially reduced by heating the engine and pressurizing the fuel. However, this can be difficult to achieve prior to engine startup due to the large mass of the engine and the limited time and energy available before engine startup. Likewise, engine rotation is required to build fuel pressure, as the fuel pump is typically cam-driven.However, start-up time requirements may limit the number of engine rotations allowed before a first fuel injection, resulting in less than optimal fuel pressures at engine start.

[0023] In hybrid vehicle systems, the engine remains off until energy for acceleration (in addition to the energy provided by the vehicle's electric motor) is required. The inventors herein have recognized that the delay experienced in transitioning from an engine-off mode (e.g., electric mode) to an engine-on mode (e.g., an auxiliary mode) in a hybrid vehicle may be sufficient to opportunistically prepare the engine for the imminent engine restart. In particular, during this time delay, the engine may be slowly rotated, such as at a lower speed than the speed at which the engine is rotated via an engine starter during cranking (during engine restart). The engine may be slowly rotated via the electric motor (e.g., electric motor 26) using energy from a system energy storage device (e.g., battery 54), which includes system batteries.Alternatively, the motor can be rotated during deceleration or deceleration events to recover energy that would otherwise be lost through wheel braking.

[0024] The slow rotation can allow each engine cylinder to be rotated sequentially through a cylinder compression stroke, as in Fig. 7. Consequently, heat generated by the air compressed in each cylinder during its respective compression stroke can be effectively transferred to the cylinder walls. This allows the temperature of the cylinder walls and the temperature of the cylinder charge to quickly equalize and allows the cylinder piston to be heated. In another example, the engine can be slowly oscillated (i.e., a direction of rotation can be changed frequently while the engine is slowly rotated) so that each cylinder can go through the compression stroke. In this way, the engine can be rotated slowly so that all of the engine's cylinders can be heated before an engine restart. During the subsequent engine restart, when fuel injection resumes, the fuel impinging on the warmer cylinder walls can result in reduced soot emissions.In addition, the numerous slow rotations can allow the fuel rail pressure to be raised sufficiently, thereby improving the spray characteristics of the fuel injector.

[0025] Fig. 2 schematically shows aspects of an exemplary engine system 200. In one example, the engine system 200 may be included in the drive system 100 of the Fig. 1, such as the engine system 5. The engine system 200 includes an engine 10. In the illustrated embodiment, the engine 10 is a boosted engine coupled to a turbocharger 13 including a compressor 114 driven by a turbine 116. In particular, fresh air is introduced along an intake passage 142 into the engine 10 via an air cleaner 112 and flows to the compressor 114. The intake passage 142 may optionally include an intake air heater 118, as shown in the illustrated embodiment, to heat intake air supplied to the engine.

[0026] In the illustrated embodiment, the compressor 114 is an electrically actuated intake air compressor that may be driven by actuating the electric motor 117, for example, if the compressor is configured as an engine-driven or driveshaft-driven supercharger compressor. In other examples, the compressor 114 may be a turbocharger compressor mechanically coupled to the turbine 116 via a shaft (not shown), with the turbine 116 driven by expanding engine exhaust. In one embodiment, the compressor and turbine may be coupled to a twin-scroll turbocharger. In another embodiment, the turbocharger may be a variable geometry turbocharger (VGT), in which the turbine geometry is actively varied as a function of engine speed.

[0027] The compressor 114 is coupled to the throttle valve 20 through the charge air cooler (CAC) 117 (also referred to herein as an intercooler). The throttle valve 20 is coupled to the engine intake manifold 23. An auxiliary air induction system (AIS) throttle 230 may also be coupled to the engine intake, upstream of the compressor 114 and upstream of the intake throttle 20. The pressure of the air charge within the intake manifold is sensed by the manifold air pressure (MAP) sensor 124. From the compressor, the compressed air flows through the charge air cooler 117 and the throttle valve into the intake manifold. Because flow through the compressor can heat the compressed air, the downstream CAC 117 is provided so that amplified intake air charge can be cooled before being delivered to the engine intake. The charge air cooler can be an air-to-water heat exchanger, for example.As set forth herein, during selected engine restart conditions, selective compressor operation may be advantageously used to heat the engine.

[0028] One or more sensors may be coupled to an inlet of the compressor 114. For example, a temperature sensor 55 may be coupled to the inlet to measure a compressor inlet temperature, and a pressure sensor 56 may be coupled to the inlet to measure a compressor inlet pressure. As another example, a humidity sensor 57 may be coupled to the inlet to determine a humidity of an air charge entering the compressor. Still other sensors may include, for example, air-fuel ratio sensors, etc. In other examples, one or more of the compressor inlet conditions (e.g., humidity, temperature, pressure, etc.) may be inferred based on the engine operating conditions.In addition, when EGR is activated, the sensors can determine the temperature, pressure, humidity, and air-fuel ratio of the air-charge mixture, which includes fresh air, recirculated compressed air, and exhaust gas residues, received at the compressor inlet.

[0029] During select conditions, e.g., during throttle release, when transitioning from boosted engine operation to unboosted engine operation, compressor surge may occur. This is due to an increased pressure differential created across the compressor as the throttle closes during throttle release. The increased pressure differential reduces forward flow through the compressor, causing surge and reduced turbocharger performance. In addition, surge may lead to NVH issues such as undesirable noise from the engine intake system. To reduce boost pressure and reduce compressor surge, at least a portion of the air charge compressed by the compressor 114 may be recirculated to the compressor inlet. This allows excessive boost pressure to be immediately and substantially reduced.The compressor recirculation system may include a compressor return passage for returning cooled compressed air from the compressor outlet, downstream of the charge air cooler 117, to the compressor inlet. In some embodiments, an additional compressor return passage (not shown) may be provided for returning uncooled (or warm) compressed air from the compressor outlet, upstream of the charge air cooler 117, to the compressor inlet.

[0030] A compressor return valve (CRV) 172 may be coupled to the compressor return passage (also referred to herein as a compressor bypass) to control an amount of cooled compressor flow returned to the compressor inlet. The CRV 172 may be configured as an on / off valve whose position is varied between an open and a closed position. Alternatively, the CRV 172 may be configured as a continuously variable valve, wherein a position of the valve can be continuously varied between the fully closed position and the fully open position. The CRV 172 may be positioned in a passage 170 downstream of the CAC 117 and upstream of an inlet of the compressor 114. A position of the CRV 172 may be adjusted during boosted engine operation to improve peak power and provide surge limit.In one example, the CRV 172 may be kept closed during boosted engine operation to improve boost response and peak power. In another example, the CRV 172 may be kept partially open during boosted engine operation to provide some surge margin, particularly an improved soft surge margin.

[0031] As discussed herein, compressor recirculation may also be used during conditions in which the engine is not combusting. Specifically, during conditions in which the engine cylinders are heated via selective operation of the compressor 114, the CRV 172 may be kept open to increase recirculation of the heated charge to the compressor, thereby causing the CAC 117 to be heated using compressor energy.

[0032] Surging may also be reduced by reducing exhaust pressure at turbine 116. For example, a wastegate actuator 92 may be actuated open to vent at least some exhaust pressure from upstream of the turbine to a downstream position via wastegate 90. By reducing the exhaust pressure upstream of the turbine, turbine speed may be reduced, which in turn helps reduce compressor surge. However, due to the gain dynamics of the wastegate, the effects of compressor recirculation valve timing on reducing surge may be faster than the effects of wastegate timing.

[0033] The intake manifold 23 is coupled to a series of combustion chambers 30 through a series of intake valves (in Fig. 3). The combustion chambers are further coupled to the exhaust manifold 25 via a series of exhaust valves (in Fig. 3). In the illustrated embodiment, a single exhaust manifold 25 is shown. However, in other embodiments, the exhaust manifold may include a plurality of exhaust manifold sections. Configurations with a plurality of exhaust manifold sections allow wastewater from different combustion chambers to be directed to different locations in the engine system.

[0034] Combustion chambers 30 may be supplied with one or more fuels, such as gasoline, alcohol blends, diesel, biodiesel, compressed natural gas, etc., via injector 66. Fuel may be delivered to the combustion chambers via direct injection, port fuel injection, throttle valve injection, or any combination thereof. Combustion in the combustion chambers may be initiated via spark ignition and / or compression ignition.

[0035] As in Fig. 2, the exhaust gas from the one or more exhaust manifold sections is directed to the turbine 116 to drive the turbine. If reduced turbine torque is desired, some exhaust gas may instead be directed through the wastegate 90, bypassing the turbine. The combined flow from the turbine and wastegate then flows through the emissions control device (ECD) 170. Generally, one or more emissions control devices 170 may include one or more exhaust aftertreatment catalysts configured to catalytically treat the exhaust stream and thereby reduce an amount of one or more substances in the exhaust stream. For example, an exhaust aftertreatment catalyst may be configured to x from the exhaust stream when the exhaust stream is lean, and the captured NO xto reduce when the exhaust flow is rich. In other examples, an exhaust aftertreatment catalyst may be configured to reduce NO x to disproportionate or NO x using a reducing agent. In still other examples, an exhaust aftertreatment catalyst may be configured to oxidize residual hydrocarbons and / or carbon monoxide in the exhaust stream. Various exhaust aftertreatment catalysts having any such functionality may be disposed in washcoats or elsewhere in the exhaust aftertreatment stages, either separately or together. In some embodiments, the exhaust aftertreatment stages may include a regenerable soot filter configured to capture and oxidize soot particulates in the exhaust stream.

[0036] As such, one or more of the exhaust catalysts of emissions control device 170 may require thermal activation. In particular, the catalyst may need to be heated to or above a light-off temperature, above which the catalyst is catalytically active. While this heat is provided by the exhaust gas released from cylinder combustion during engine operation, during engine restart, the temperature of the catalyst may be below its activation temperature. In some embodiments, to accelerate activation of the exhaust catalyst to improve emissions at engine start-up, emissions control device 170 may be coupled to an exhaust catalyst heater 121.

[0037] All or a portion of the treated exhaust gas from the emission control device 170 may be released to the atmosphere via an exhaust conduit 35. However, depending on operating conditions, a portion of the exhaust residue may instead be diverted into the EGR passage 150, through the EGR cooler 151 and the EGR valve 152, to the inlet of the compressor 114. As such, the EGR passage 150 is configured as a low-pressure EGR passage that couples the engine exhaust manifold, downstream of the turbine 116, to the engine intake manifold, upstream of the compressor 114. In the illustrated example, the EGR passage is shown coupled to the compressor inlet, independent of the compressor return passage. In other examples, however, the EGR passage 150 may coincide with the compressor return passage, upstream of the compressor inlet.Also in the example shown, the EGR passage 150 is shown receiving exhaust residuals at a location downstream of the emissions control device 170. It should be understood that in other examples, the EGR passage 150 may be configured to receive exhaust residuals at a location upstream of the emissions control device 170. In still other embodiments, the engine system 100 may additionally or optionally include a high-pressure EGR system coupling the engine exhaust manifold upstream of the turbine 116 to the engine intake manifold downstream of the compressor 114.

[0038] The EGR valve 152 can be opened to admit a controlled amount of cooled exhaust gas to the compressor inlet for desired combustion and emissions control performance. In this way, the engine system 10 is adapted to provide external low-pressure EGR (LP) by capturing exhaust gas from after the turbine 116. The EGR valve 152 can also be a continuously variable valve or an on / off valve. The rotation of the compressor, in addition to the relatively long LP EGR flow path in the engine system 10, provides excellent homogenization of the exhaust gas into the intake air charge. Furthermore, the provision of EGR starting and mixing points provides very effective cooling of the exhaust gas for increased available EGR mass and improved power.

[0039] The EGR cooler 151 may be coupled to the EGR passage 150 to cool EGR supplied to the compressor. Additionally, one or more sensors may be coupled to the EGR passage 150 to provide details regarding the composition and condition of the EGR. For example, a temperature sensor may be provided to determine a temperature of the EGR, a pressure sensor may be provided to determine a pressure of the EGR, a humidity sensor may be provided to determine a humidity or water content of the EGR, and an air-fuel ratio sensor 154 may be provided to determine an air-fuel ratio of the EGR. Alternatively, EGR conditions may be derived from the one or more temperature, pressure, humidity, and air-fuel ratio sensors 55-57 coupled to the compressor inlet.EGR valve opening can be adjusted based on engine operating conditions and EGR conditions to provide a desired amount of engine dilution.

[0040] As discussed herein, during conditions where the engine is not combusting, the EGR valve may be opened to accelerate cylinder warm-up. In particular, during conditions where the engine is slowly rotated by electric motor torque prior to engine restart and / or while the compressor is rotated via its electric motor, the EGR valve 152 is held fully open so that air charge heated in the cylinders during a compression stroke or heated via compressor energy can be recirculated through the engine. By simultaneously holding the AIS throttle 230 fully closed, the exhaust flow is restricted and the hot air is kept within the engine. In other words, the hot air can be pumped through the engine in a loop.By additionally operating one or more of the intake heaters 118 and the exhaust catalyst heaters 121, heat transfer to the cylinders can be further enhanced. As shown in . Fig. 6, based on the need for piston heating, the engine system can be operated in one of several modes, using various combinations of compression heating to heat the cylinders. For example, if more heating is required while rotating the compressor 114 via the electric motor 117, the CRV 172 can be opened while also operating the intake heater 118 and the exhaust catalyst heater 121. Additionally, the engine can be rotated without fuel via the torque of the electric motor, either continuously during compressor rotation or intermittently.

[0041] The engine system 200 may further include a control system 14. The control system 14 is illustrated receiving information from a plurality of sensors 16 (various examples of which are described herein) and sending signals to a plurality of actuators 81 (various examples of which are described herein). The sensors 16 may include, for example, an exhaust gas sensor 126 located upstream of the emissions control device, a MAP sensor 124, an exhaust gas temperature sensor 128, an exhaust gas pressure sensor 129, a compressor inlet temperature sensor 55, a compressor inlet pressure sensor 56, a compressor inlet humidity sensor 57, and an EGR sensor 154. Other sensors, such as additional pressure, temperature, air-fuel ratio, and composition sensors, may be coupled at various locations in the engine system 200. The actuators 81 may, for example,a throttle 20, an EGR valve 152, a compressor recirculation valve 172, a wastegate 92, and a fuel injector 66. The control system 14 may include a controller 12. The controller may receive input data from the various sensors, process the input data, and trigger various actuators in response to the processed input data based on a command or code programmed therein corresponding to one or more routines.

[0042] Fig. 3 shows an exemplary embodiment of a combustion chamber or cylinder of the engine 10 (the Fig. 1-2). The engine 10 may receive control parameters from a control system including a controller 12 and inputs from an operator 130 of the vehicle via an input device 132. In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. The cylinder (herein also the "combustion chamber") 30 of the engine 10 may include combustion chamber walls 236 with a piston 238 disposed thereon. The piston 238 may be coupled to a crankshaft 240 such that the piston movement of the piston is translated into a rotational movement of the crankshaft. The crankshaft 240 may be coupled to at least one drive wheel of the passenger vehicle via a transmission system. Further, a starter motor may be coupled to the crankshaft 140 via a flywheel to activate a starting operation of the engine 10. In particular, the generator 24 (the Fig. 1) and the final drive, which drives the electric motor 26 (the Fig. 1) be coupled to the crankshaft to provide torque for the cranking power of the engine.

[0043] Cylinder 30 may receive intake air via a series of intake air passages 242, 244, and 246. Intake air passage 246 may communicate with other cylinders of engine 10 in addition to cylinder 30. In some embodiments, one or more of the intake passages may include a charging device such as a turbocharger or a supercharger. For example, FIG. Fig. 3 shows an engine 10 configured with a turbocharger comprising an electrically actuated compressor 274 disposed between intake ports 242 and 244 and an exhaust turbine 276 disposed along exhaust port 248. Compressor 274 may be driven at least partially by exhaust turbine 276 via a shaft 280, wherein the charging device is configured as a turbocharger. In other examples, such as when engine 10 is provided with a supercharger, exhaust turbine 276 may optionally be omitted, wherein compressor 274 may be driven by an electric motor. A throttle 20, comprising a throttle plate 164, may be provided along an intake port of the engine to vary the flow rate and / or pressure of the intake air provided to the engine cylinders. For example, throttle 20 may be disposed downstream of compressor 274, as shown in Fig. 3, or alternatively, it may be arranged upstream of the compressor 174. In some embodiments, as described with reference to Fig. 2, a charge air cooler (CAC 117) may be positioned downstream of the compressor 274 and upstream of the throttle 20 to cool a supercharged air charge supplied to the engine. Alternatively, the CAC 117 may be positioned downstream of the throttle, integrated into the intake manifold 246.

[0044] Exhaust passage 248 may receive exhaust gases from other cylinders of engine 10 in addition to cylinder 30. Exhaust sensor 128 is coupled to exhaust passage 148 and is shown upstream of emissions control device 170. Sensor 128 may be selected from various suitable sensors to provide an indication of air-fuel ratio, such as a linear oxygen sensor or UEGO (wideband oxygen sensor), a dual-state oxygen sensor or EGO (as shown), a HEGO (heated EGO), a NOx, HC, or CO sensor. Emissions control device 170 may be a three-way catalyst (TWC), NOx trap, various other emissions control devices, or combinations thereof.

[0045] The exhaust temperature may be measured by one or more temperature sensors (not shown) disposed in the exhaust passage 248. Alternatively, the exhaust temperature may be derived based on engine operating conditions such as speed, load, air-fuel ratio (AFR), spark retard, etc. Further, the exhaust temperature may be calculated by one or more exhaust sensors 128. It should be understood that the exhaust temperature may alternatively be determined using any combination of the temperature determination methods listed herein.

[0046] Each cylinder of engine 10 may include one or more intake valves and one or more exhaust valves. For example, cylinder 30 is illustrated as including at least one intake poppet valve 250 and at least one exhaust poppet valve 256 disposed in an upper region of cylinder 30. In some embodiments, each cylinder of engine 10, including cylinders 30, may include at least two intake poppet valves and at least two exhaust poppet valves disposed in an upper region of the cylinder.

[0047] Intake valve 250 may be controlled by controller 12 through cam actuation via cam actuation system 251. Likewise, exhaust valve 256 may be controlled by controller 12 via cam actuation valve 253. Cam actuation systems 251 and 253 each include one or more cams, and they may include one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (WL) systems operable by controller 12 to vary valve operation. The position of intake valve 250 and exhaust valve 256 may be determined by valve position sensors 255 and 257, respectively. In alternative embodiments, the intake and / or exhaust valves may be controlled using electrical valve actuation. For example, cylinder 30 canAlternatively, an intake valve controlled by electric valve actuation and an exhaust valve controlled by cam actuation, including CPS and / or VCT systems. In still other embodiments, the intake and exhaust valves may be controlled by a common valve actuation device or system, or a variable valve timing actuation device or system.

[0048] Cylinder 30 may have a compression ratio that is the volumetric ratio when piston 238 is at the bottom center to top center position. Conventionally, the compression ratio is in the range of 9:1 to 13:1. However, in some examples where different fuels are used, the compression ratio may be increased. This may be the case, for example, when using higher octane fuels or fuels with higher latent enthalpy of evaporation. The compression ratio may also be increased when direct injection is used due to its effect on engine knock.

[0049] In some embodiments, each cylinder of engine 10 may include a spark plug 192 for initiating combustion. Ignition system 190 may provide an ignition spark to combustion chamber 30 via spark plug 192 in response to the pre-ignition (Sa) signal from controller 12 under selected operating modes. However, in some embodiments, spark plug 192 may be omitted, such as when engine 10 is capable of initiating combustion via auto-ignition or by injecting a fuel, as may be the case with many diesel engines.

[0050] In some embodiments, each cylinder of engine 10 may be configured with one or more injectors to provide a fluid that suppresses knock or pre-ignition. In some embodiments, the fluid may be a fuel, where the injector is also referred to as a fuel injector. As a non-limiting example, cylinder 30 is shown including a fuel injector 166. Fuel injector 166 is shown coupled directly to cylinder 30 to inject fuel therein in proportion to the pulse width signal FPW received from controller 12 via electronic driver 168. In this manner, fuel injector 166 provides what is known as direct injection (hereinafter also referred to as "DI") of fuel into combustion cylinder 30. While Fig. While Figure 2 shows the injector 166 as a side injector, it may also be positioned overhead of the piston, for example, near the position of the spark plug 192. Such a position may improve mixing and combustion when the engine is running on an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be positioned overhead and near the intake valve to improve mixing.

[0051] Fuel may be supplied directly to the fuel injector 166 from a high-pressure fuel system 8, which includes fuel tanks, fuel pumps, and a fuel rail. Alternatively, the fuel may be supplied from a lower-pressure, single-stage fuel pump, in which case the timing of direct injection of fuel during the compression stroke may be more limited than when a high-pressure fuel system is used. Further, although not shown, the fuel tanks may include a pressure transducer that provides a signal to the controller 12. It should be understood that in another embodiment, the injector 166 may be a port injector that provides fuel into the intake manifold upstream of the cylinder 30.

[0052] As shown above, Fig. 3 only one cylinder of a multi-cylinder engine. As such, each cylinder may also include its own set of intake / exhaust valves, fuel injector(s), spark plugs, etc.

[0053] Fuel tanks in the fuel system 8 may hold fuels of different qualities, such as different compositions. These differences may include different alcohol content, different octane rating, different heat of vaporization, different fuel blends and / or combinations thereof, etc. In one example, fuels with different alcohol contents could include one fuel that is gasoline and the other that is ethanol or methanol. In another example, the engine may use gasoline as a first substance and an alcohol-containing fuel blend such as E85 (which is approximately 85% ethanol and 15% gasoline) or M85 (which is approximately 85% methanol and 15% gasoline) as a second substance.

[0054] Further, in the disclosed embodiments, an EGR system may direct a desired portion of the air charge or exhaust gas from the exhaust passage 248 to the air induction passage 242. Fig. 3 shows an LP-EGR system wherein LP-EGR is routed through LP-EGR passage 260 from after turbine 276 to before compressor 274. The amount of LP-EGR provided to intake passage 242 may be varied by controller 12 via LP-EGR valve 262. Similarly, an HP-EGR system (not shown) may be provided in which HP-EGR is routed through an HP-EGR passage from before turbine 276 to after compressor 274. The amount of HP-EGR provided to intake passage 146 may be varied by controller 12 via a dedicated HP-EGR valve. The HP EGR system may include an HP EGR cooler, and the LP EGR system may include an LP EGR cooler 266 to reject heat from the EGR gases, e.g., to the engine coolant.

[0055] EGR sensors may be disposed within the EGR passages and may indicate one or more of mass flow, pressure, temperature, O2 concentration, and exhaust gas concentration. In some embodiments, one or more sensors may be disposed within the LP EGR passage 260 to indicate one or more of pressure, temperature, and air-fuel ratio of the exhaust gas recirculated through the LP EGR passage. Exhaust gas redirected through the LP EGR passage 260 may be diluted with fresh intake air at a mixing point located at the junction of the LP EGR passage 260 and the intake passage 242. In particular, dilution of the EGR flow may be adjusted by adjusting the LP EGR valve 262 in coordination with a low-pressure air induction system (LP AIS) throttle 230. A percentage dilution of the LP EGR stream can be derived from the output of a sensor 265 in the EGR gas stream.

[0056] The control 12 is in Fig. 3 as a microcomputer comprising a microprocessor unit 206, input / output ports 208, an electronic storage medium for executable programs and calibration values ​​shown as a read-only memory chip 210 in this particular example, a random access memory 212, a keep-alive memory 214 and a data bus.The controller 12 may receive various signals from sensors coupled to the engine 10 in addition to those previously discussed, including the induced mass air flow (MAF) measurement from the mass air flow sensor 222; an engine coolant temperature (ECT) from the temperature sensor 216 coupled to the cooling jacket 218; a profile ignition pickup (PIP) signal from the Hall effect sensor 220 (or other type) coupled to the crankshaft 140; the throttle position (TP) from a throttle position sensor; the absolute manifold pressure (MAP) signal from sensor 124, cylinder AFR from the EGO sensor 128, and abnormal combustion from a knock sensor. The engine speed signal RPM may be generated by the controller 12 from the PIP signal. The manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum or pressure in the intake manifold.

[0057] The storage medium read-only memory 210 may be programmed with computer-readable data representing instructions executable by a processor 206 to perform the methods described below, as well as other variations that are anticipated but not specifically listed. Example routines are described herein in the Fig. 4-5 described.

[0058] With reference now to Fig. 4 shows an exemplary routine 400 for compression heating engine cylinders prior to an engine restart. In this way, soot emissions following direct fuel injection may be reduced during the subsequent engine restart.

[0059] At 402, vehicle and engine operating conditions may be determined and / or measured. These may include, for example, a brake pedal position, an accelerator pedal position, an operator torque requirement, the battery state of charge (SOC), the engine temperature (Teng), the ambient temperature and humidity, the barometric pressure (BP), etc. In one example, the hybrid vehicle system is a power-split hybrid vehicle system.

[0060] At 404, the vehicle operating mode may be determined based on the determined operating conditions. For example, based at least on the determined driver torque requirement and the battery charge status, it may be determined whether to operate the vehicle in a motor-only mode (where the engine drives the vehicle wheels), an auxiliary mode (where the battery assists the engine in driving the wheels), or an electric-only mode (in which only the battery powers the vehicle). In one example, if the desired torque can be provided only by the battery, the vehicle may be operated in electric-only mode, where the vehicle is propelled using only the torque of the electric motor.In another example, if the desired torque cannot be provided by the battery, the vehicle may be operated in motor mode or in assist mode, in which the vehicle is propelled with at least some torque from the electric motor. The vehicle may be operated accordingly in the particular operating mode.

[0061] At 406, it may be confirmed that the vehicle is in electric mode. If electric mode is not confirmed at 408, the hybrid vehicle may be propelled with at least some engine torque. For example, the vehicle may be propelled with only engine torque (e.g., in electric mode) or a combination of engine torque and electric motor torque (e.g., in assist mode). If electric mode is confirmed at 410, the routine includes propelling the hybrid vehicle using only electric motor torque.

[0062] At 412, engine cylinder temperatures may be determined, inferred, or modeled, and it may be determined whether engine heating is required to reduce emissions upon subsequent engine restart. In one example, cylinder piston temperatures may be assessed, and it may be determined that heating is required if the piston temperature is below a threshold temperature. In another example, cylinder wall temperatures may be compared to a cylinder charge temperature, and it may be determined that heating is required if the difference between the cylinder wall temperature and the cylinder charge temperature is higher than a threshold. In still further examples, while the vehicle is being propelled with electric motor torque, it may be determined whether an engine start is imminent. For example,Based on operating conditions such as driver pedal position, battery charge level, etc., it can be determined whether the engine needs to be restarted to meet the driver torque requirement. If engine cylinder temperatures indicate that further heating is not necessary and / or if an imminent engine restart is not confirmed, the routine may end.

[0063] If heating is required at 414, the controller may use any combination of engine compression heating and cylinder compression stroke heating to increase cylinder piston temperatures in anticipation of the imminent engine restart. As described in the Fig. As explained in Figures 5-6, this may involve rotating an electrically actuated intake compressor with an upstream intake throttle closed and an EGR valve open, while the hybrid vehicle is being driven by electric motor torque, until a piston temperature is higher than a threshold (or until a temperature difference between the cylinder wall and the cylinder charge is below a threshold). Here, the compressor energy is used to compress the air charge, which generates heat. This heat is then recirculated through the engine, enabling cylinder heating.

[0064] Alternatively, heating may involve rotating the engine without fuel via the torque of the electric motor at less than one engine crank speed while operating an exhaust heater or an intake heater and keeping the EGR valve open and the intake throttle closed to recirculate the heated air charge through the engine. During slow rotation, each cylinder of the engine is progressively rotated to a first position in which the cylinder is in a compression stroke and temporarily held in the first position so that a temperature of the cylinder walls and charge can be equalized. The slow rotation allows each cylinder to also rotate to the compression stroke and be temporarily held there as the cylinder becomes heated. As such, the cylinder can then be cooled as the cylinder continues to rotate into the subsequent expansion stroke.However, the cylinder can be heated more during the compression stroke than it is cooled during the expansion stroke, allowing for net cylinder heating via slow rotation. Thus, slow rotation activates a heat pump effect within the cylinder. Slow engine rotation can advantageously utilize heat generated during the compression stroke of selected cylinders to heat the combustion chamber, thereby preheating the engine before engine restart. Additionally, fuel pressure can be increased via slow engine rotation, improving fuel spray characteristics and reducing soot generation.

[0065] Other combinations are possible, as shown in the table of Fig. 6. In each case, spinning is initiated in response to the need for cylinder heating (e.g., in response to a cylinder piston temperature being lower than a threshold), and spinning continues until the piston temperature is higher than the threshold. By heating the engine before restarting, cold-start particulate emissions, which are a result of direct fuel injection onto the cold surfaces of the combustion chambers, can be reduced.

[0066] At 416, after sufficient preheating, the engine may be cranked and fueled if conditions for engine restarting are met. Optionally, the engine may be pre-primed via the electric motor. In particular, the engine may be quickly rotated without fuel to a position that improves engine restartability. For example, the engine may be rotated so quickly that an engine cylinder is at or near intake valve closing (IVC). This allows the cylinder to be compressed during the engine cranking that precedes an engine restart, and cylinder firing may occur within less than 180 degrees. In another example, the cylinder may be rotated so that the piston is at or near fueling TDC and is compressed. The cylinder may then wait for a spark.In the latter example, however, there may be some downward leakage. Once the engine is primed, the engine can be restarted when needed. For example, the engine may be restarted due to an increased need for driver torque that cannot be met via an electric motor or hybrid vehicle system battery. Alternatively, the engine may be restarted due to a drop in the battery's charge level. Additionally, the engine may be restarted to run an air compressor to meet HVAC requirements. Once the conditions for restarting the engine are met, the engine can be cranked and fueled so that engine combustion can restart.

[0067] With reference now to Fig. 5, an example routine 500 for heating the engine cylinders using compression heating prior to an engine restart to improve fuel evaporation during the restart is shown.

[0068] At 502, it may be confirmed that a heated piston is required. In one example, piston heating may be required if the cylinder piston temperature (or other cylinder combustion surface temperature) is below a threshold. In another example, piston heating may be required if a temperature difference between the cylinder walls and the cylinder charge is below a threshold. The cylinder combustion surface temperatures may be determined, inferred, or calculated in a model. If heating is not required, the routine may end.

[0069] If heating is required, the cylinder can be heated using compression heating combinations. The various combinations are listed in Table 600 of the Fig. 6, and some of the options are listed here in Fig. 5. A first set of heating operations, starting with motor rotation, is listed in steps 504-518. Another set of heating operations, starting with compressor rotation, is listed in steps 520-534.

[0070] At 504, while the hybrid vehicle is being powered only by electric motor torque and prior to an imminent engine restart, the routine includes rotating the engine without fuel via electric motor torque at less than a threshold speed. Here, the vehicle's electric motor may be powering the vehicle and rotating the engine. The threshold speed, in one example, may be an engine crank speed. This means that the engine may be rapidly spun at a speed slower than the speed at which the engine would have been rapidly spun by a starter during engine cranking and restart. For example, during engine cranking, the engine may be spun without fuel via a starter at 150 rpm. In comparison, during slow rotation to heat the cylinder, the engine may be spun at 10-30 rpm via the hybrid vehicle's electric motor / generator.In other examples, the limit speed at or below which the engine is slowly rotated may be higher or lower based on operating parameters such as oil temperature, ambient temperature, or NV.

[0071] In one example, slow rotation of the engine may be initiated in a cylinder (e.g., a first cylinder) selected based on proximity of a cylinder piston position relative to a compression stroke TDC. For example, a controller may identify a cylinder whose piston is located closest to the compression stroke TDC or at a position where at least a threshold level of compression is experienced. The engine is then rotated such that each cylinder is sequentially heated during a compression stroke of the cylinder. As rotation continues, each cylinder may be cooled during an expansion stroke of the cylinder immediately following the compression stroke. However, the cylinder may be heated more during the compression stroke than the cylinder is cooled during the expansion stroke, allowing for a net heating of each cylinder via a heat pump effect.As such, during a compression stroke of each cylinder, the air charge can be compressed, generating heat. Rotating an engine so that a cylinder is kept in the compression stroke allows heat to be transferred from the compressed air to the cylinder walls, cylinder head, and piston, increasing the engine temperature.

[0072] In some examples, the motor may be opportunistically rotated via vehicle wheels. For example, the controller may determine if a reduction in vehicle speed is occurring, such as during a vehicle braking or deceleration event. If so, the motor may be rotated via the wheels during the vehicle braking or deceleration event. In this case, the torque from the wheels, which would otherwise be lost as heat or used for regenerative braking, can be advantageously used to rotate the motor. Motor rotation via the vehicle wheels may be used instead of, or in addition to, motor rotation via the torque of the electric motor. For example,During one of the vehicle braking and deceleration events, the engine rotation speed may be temporarily increased by rotating the engine via the hybrid vehicle's wheels and the engine's electric motor.

[0073] At 506, the routine includes an upstream intake throttle (such as the AIS throttle 230 of the Fig. 2-3) is kept closed during rotation. The intake throttle, which is closed, can be located upstream of the intake compressor.

[0074] Closing the intake throttle allows compressed air charge to be drawn back into the engine without net outflow of exhaust gas. As such, this reduces the possibility of emissions that may be trapped in the crankcase. At 508, the routine further includes an EGR valve (such as EGR valve 152 of Fig. 2) is held open to recirculate heated air charge through the engine. By rotating the engine while closing the AIS throttle and holding the EGR valve open, air can be pumped through the engine cylinders. Opening the EGR valve recirculates flow from the cylinder back to the engine, reducing engine vacuum. Here, air is pumped in a closed loop. By allowing the heat of compression at TDC to be removed after expansion, the charge is made cooler than when compression started. The charge can then be expelled from the engine's exhaust pipe or recirculated through the EGR system so that the same charge is used over and over again. This limits the potential for hydrocarbons in the exhaust.

[0075] At 512, the routine optionally includes, while rotating the engine, operating an exhaust catalyst (such as the exhaust catalyst 121 of the Fig. 2) coupled exhaust heater. At 514, the routine optionally includes, during rotation, operating an intake heater coupled in an intake passage of the engine (such as intake heater 118 of Fig. 2). By operating one or more of the intake and exhaust heaters, additional heat is deposited into the charge passing through the engine's cylinders, thereby improving the transfer of heat to the cylinder combustion surfaces.

[0076] At 516, the routine optionally includes operating an electrically actuated compressor coupled to an intake of the engine. By rotating the compressor, additional heat is provided via compressor energy into the heated compressed air charge. While rotating the electrically actuated compressor, the controller may adjust cam timing (e.g., a VCT position) to increase positive intake-exhaust valve overlap. For example, intake and / or exhaust valve timing may be adjusted to a position that enhances blowthrough of the compressed air charge through the engine cylinders. This enhances heat transfer from the compressed air charge to the engine cylinders.

[0077] At 518, the routine optionally further includes, while the electrically actuated compressor is operating, opening a compressor return valve (such as the CRV 172 of Fig. 2), which is coupled via the compressor. By opening the CRV 172, the CAC 117 can also be heated via compressor energy. The rotation of the engine and / or the rotation of the compressor can then continue until the cylinders are sufficiently warm.

[0078] In an alternative heating option at 520, the routine includes rotating the engine via the electric motor to a position with a more positive valve overlap for increased blow-by capabilities. For example, cam timing or valve timing may be adjusted to increase positive valve overlap. At 522, while the hybrid vehicle is propelled using torque from the electric motor, the routine includes rotating an electrically actuated intake compressor. Rotating the electrically actuated intake compressor may include activating an electric motor coupled to the compressor. Additionally, the compressor may be rotated at less than a threshold speed required for boost buildup.The electric motor coupled to the compressor may be a first electric motor that is different from a second electric motor (or electric motor / generator) used to power the hybrid vehicle.

[0079] At 524, while the compressor is rotating, an upstream intake throttle may be closed. Specifically, an AIS throttle coupled upstream of the compressor is closed. At 526, an EGR valve is held open during rotation. Closing the intake throttle allows the compressed air charge to be drawn back into the engine without any net flow out of the exhaust. By opening the EGR valve, flow out of the cylinder is directed back into the engine, reducing engine vacuum. By rotating the compressor while the AIS throttle is closed and the EGR valve is held open, air can be pumped through the engine cylinders. Thus, air is pumped in a closed loop. By allowing the heat of compression at TDC to be removed after expansion, the charge is made cooler than at the start of compression.The charge can then be forced out the engine exhaust, or it can be recirculated through the EGR system so that the same charge is reused over and over again. This limits the potential for hydrocarbons in the exhaust. The EGR valve can be positioned in a low-pressure EGR passage that couples an engine exhaust, downstream of an exhaust catalyst, with an engine intake, upstream of the supercharger.

[0080] At 528, the routine optionally includes activating an electric heater coupled to an exhaust catalyst during rotation. At 530, the routine optionally includes operating an electric heater coupled in an intake passage of the engine during rotation. By operating one or more of the intake and exhaust heaters, the air charge looped through the engine may be further heated.

[0081] At 532, the routine optionally includes, while rotating the compressor, opening a recirculation valve coupled in a compressor bypass passage across the compressor to increase recirculation through a charge air cooler coupled downstream of the compressor.

[0082] At 534, the routine optionally includes, while rotating the compressor, continuing to rotate the engine without fuel via electric motor torque. For example, the engine may be rotated via electric motor torque from the second electric motor at less than engine crank speed. By rotating the engine, each engine cylinder is exposed to hot blowby air from the compressor. The engine may be rotated continuously or intermittently at the reduced speed. For example, the engine may be rotated periodically to disperse compressor heat.

[0083] In each case, the rotating occurs in response to a detected cylinder piston temperature being lower than a threshold temperature. Furthermore, in each case, the rotating may continue until the engine cylinder is sufficiently heated. For example, it may be determined whether a piston temperature is higher than a threshold value, or whether a temperature difference between the cylinder walls and the cylinder charge is lower than a threshold value. In another example, the engine temperature or an average cylinder piston temperature may be assessed (e.g., compared to a threshold temperature). If the piston temperature is higher than the threshold, or if the difference is lower than the threshold, then rotation of the compressor and / or the engine may be interrupted, and fuel injection into the cylinder may be resumed to restart the engine.Otherwise, rotation of the engine and / or compressor may continue until the piston temperature is at or above the limit temperature (or until the temperature difference between the cylinder walls and the cylinder charge is lower than a limit value, or until the engine temperature or the average cylinder piston temperature is higher than the limit temperature).

[0084] In some examples, control may also determine if an engine fuel rail pressure is greater than a threshold pressure. The rotation of the engine may then be adjusted based on the fuel rail pressure determination. In particular, if the fuel rail pressure is not sufficiently high, control may maintain the unfueled engine rotation at less than the threshold speed until the fuel rail pressure is above the threshold pressure. However, because the fuel rail pressure may build up within a number (e.g., five to ten) of engine pumping strokes, and because a threshold number of pumping strokes (e.g., two) are reached during each engine revolution, the fuel rail pressure may reach the threshold pressure when the cylinder temperature has been sufficiently raised.

[0085] After all engine cylinders have been warmed up, if the restart conditions are met, fuel injection to the cylinder may be resumed to restart the engine. For example, the engine may be rotated at engine crank speed via an engine starter. The controller may then select an engine cylinder in which to resume fueling the cylinder. The cylinder may be selected based on piston position. For example, a cylinder that is at or near IVC may be selected. Fuel may then be injected into the selected cylinder during engine cranking to restart the engine. It should be understood that in another example, the engine may not select an engine cylinder to resume fueling the cylinder, but fueling may be resumed as needed.

[0086] It should be understood that in further examples, after slowly rotating the engine to warm the cylinder, the routine may further include rotating the engine without fuel via the vehicle's electric motor to a position optimal for restartability of the engine. For example, the engine may be rotated to a position where the engine can be quickly restarted if the conditions for restarting the engine are not met immediately after the cylinder is warmed. In one example, further rotating may include rotating to a position where an engine cylinder is at or near IVC.

[0087] In this way, a hybrid vehicle method is provided for heating engine cylinders in response to a cylinder wall temperature being lower than a limit while the vehicle is being propelled using electric motor torque alone. Therein, during a first condition, a controller is configured with computer-readable instructions stored on non-transitory memory including code to rotate the engine without fuel using electric motor torque at less than crank speed to sequentially heat all engine cylinders as they undergo a compression stroke. In comparison, during a second condition, the controller is configured with code to rotate an electrically actuated intake compressor with a compressor return valve held open.During both the first and second conditions, an intake throttle is held closed, and an EGR valve is held open. In addition, during both the first and second conditions, spinning continues until the cylinder wall temperature is above the limit, where the limit is based on the cylinder charge temperature. Further, during each of the first and second conditions, one or more of an exhaust heater and an intake heater may be operated, wherein the exhaust heater is coupled to an exhaust catalyst disposed upstream of an EGR passage inlet and the intake heater is coupled to an intake passage upstream of the compressor.

[0088] Fig. Figure 7 graphically shows the compression stroke heating effect on map 700. In particular, a first set of plots 702-704 are shown, which represent the change in in-cylinder temperature as the cylinder is rotated through the compression stroke. A second set of plots 712-714 show the change in in-cylinder pressure as the cylinder is rotated through the compression stroke. In the example shown, the engine is slowly rotated at 30 rpm. In each set, plots 702 and 712 (solid lines) show the calculated data, while plots 704 and 714 (dashed lines) show the simulated data. The calculated data represents a scenario in which no heat flows and no heat is transferred to the cylinder walls and piston.In comparison, the simulated data represents a scenario in which heat flows and is transferred to the cylinder walls and piston. The ideal curves shown start at intake valve closing (IVC; at approximately 625 CAD) and end at exhaust valve opening (EVO; at approximately 832 CAD). The calculated curves (plots 704, 714) were based on the isentropic process and the volume ratio. The ideal curves (plots 702, 712) are then recalculated using P1 and V1 of the isentropic process and the volume ratio at IVC. As can be seen, significant amounts of heat are transferred to the cylinder walls and pistons during the compression stroke, although some cooling occurs after the compression stroke. In particular, the simulated data shows how heat is lost from the compressed air as it flows to the cylinder walls and pistons, with a subsequent drop in in-cylinder temperature.Furthermore, the heat is transferred directly to the point where heat transfer has a significant effect on particulate matter emissions. This heat transfer is used to advantageously raise the piston temperature. Specifically, compression stroke heating is repeated over several cycles until the piston temperature is above a threshold temperature. Thus, during slow engine rotation, each cylinder is allowed to heat during that cylinder's compression stroke. Consequently, when the engine is restarted and fuel is supplied to the preheated cylinder, the liquid fuel droplets can directly impinge on the hot combustion surfaces, resulting in enhanced fuel evaporation.

[0089] With reference now to Fig. 6, the table shows 600 different engine operating or heating modes that can be used in the hybrid vehicle system of the Fig. 1-3 may be possible. As such, the modes presented may be non-limiting examples, and additional modes are possible.

[0090] In one example, the engine system may be operated in a first mode (Mode 1), in which the engine is slowly rotated without fuel via electric motor torque while an intake throttle is closed and an EGR valve is kept open. Here, the engine cylinders are heated using heat generated in the compression stroke.

[0091] In another example, the engine system may be operated in a second mode (Mode 2) in which, in addition to the settings of the first mode, an electric intake heater may be operated for additional charge heating. Alternatively, the engine system may be operated in a third mode (Mode 3) in which, in addition to all of the settings of the first mode, an electric exhaust catalyst heater may be operated for additional charge heating. Further, the engine system may be operated in a fourth mode (Mode 4) in which, in addition to all of the settings of the first mode, both the intake heater and the exhaust catalyst heater may be operated for additional charge heating.

[0092] In another example, the engine system may be operated in a fifth mode (Mode 5) in which, in addition to all of the settings of the first mode, an electrically actuated supercharger may be operated. This means that each of the engine and the supercharger may be rotated in the fifth mode (and in modes related to the fifth mode). In addition, during the fifth mode, the valve timing may be adjusted so that the engine operates with valve overlap. By adjusting the cam timing to increase the positive intake valve-exhaust valve overlap, improved blow-through of air (compressed and heated by the supercharger) through the engine cylinders is provided. During a sixth mode (Mode 6), the engine may operate with all of the settings of the fifth mode and with the compressor return valve (CRV) open to increase recirculation of the heated charge across the supercharger.This allows the downstream CAC 117 to be heated with the compressor energy.

[0093] The engine can alternatively be operated in a seventh mode (Mode 7), in which, in addition to all the settings of the fifth mode, the electric intake heater can be operated for additional charge heating. In the eighth mode (Mode 8), the engine can be operated with all the settings of the seventh mode and with the CRV additionally open. The engine can alternatively be operated in a ninth mode (Mode 9), in which, in addition to all the settings of the fifth mode, the exhaust catalyst heater can be operated for additional charge heating. In the tenth mode (Mode 10), the engine can be operated with all the settings of the ninth mode and with the CRV additionally open.

[0094] The engine may also be operated in an eleventh mode (Mode 11) in which each of the motor and compressor is rotated, each of the intake and exhaust heaters is operated, each of the CRV and EGR valves is held open while the intake throttle is held closed, and the engine cam timing is adjusted to allow blow-by.

[0095] The engine can also be operated in a twelfth mode (Mode 12), where heating of the piston is provided by rotating only the compressor. Here, positive valve overlap is maintained while the intake throttle is closed and the EGR valve is opened. Alternatively, the engine system can be operated in a thirteenth mode (Mode 13), in which, in addition to all the settings of the twelfth mode, the CRV can be opened. The engine can also be operated in a fourteenth mode (Mode 14), in which, in addition to rotating the compressor as per the twelfth mode setting, the CRV can be held open and the intake heater can be operated, or in a seventeenth mode (Mode 17), in which, in addition to rotating the compressor as per the twelfth mode setting, the CRV can be held open and the intake heater can be operated.Likewise, the engine can be operated in a fifteenth mode (Mode 15) in which, in addition to rotating the compressor as per the twelfth mode setting, the CRV can be kept open and the exhaust heater can be operated, or in an eighteenth mode (Mode 18) in which, in addition to rotating the compressor as per the twelfth mode setting, the CRV can be kept closed and the exhaust heater can be operated. The engine can also be operated in a sixteenth mode (Mode 16) in which, in addition to all the settings of the twelfth mode, both the intake heater and the exhaust catalyst heater can be operated for additional charge heating and the CRV can be kept open.Finally, the engine can also be operated in a twentieth mode (Mode 20), in which both the intake heater and the exhaust catalyst heater can be operated during compressor rotation and the CRV can be kept closed.

[0096] While the modes illustrated above show the intake throttle closed and the EGR valve open during rotation of the engine and / or compressor, in still other modes the intake throttle may be open and / or the EGR valve may be closed.

[0097] A controller can select between the different modes based on how much cylinder heating is required. The selection can further be based on factors such as the battery charge level (e.g., how long the electric motor can operate), a time interval until an imminent engine restart, vehicle speed, etc. Likewise, the controller can transition between modes as heating requirements change. For example, when piston temperatures are colder, the controller can initiate operation in one of modes 5-11, rotating both the motor and compressor. When the heating requirement drops, the controller can transition to rotating with either just the motor (as in modes 1-4) or just the compressor (as in modes 12-10).In another example, when temperatures are colder, the controller may initiate operation in one of the modes, with both the intake heater and the exhaust heater operating. If the heating demand decreases, the controller may transition to operation with only one of the intake heater and the exhaust heater activated.

[0098] An example of engine cylinder heating via combinations of engine rotation, compressor rotation, compressor recirculation and exhaust gas recirculation is now shown on map 800 of the Fig. 8. Map 800 shows vehicle speed at plot 802, compressor rotational speed at plot 804, battery state of charge (SOC) at plot 806, cylinder piston temperature at plot 808, engine speed at plot 810, fuel rail pressure at plot 812, AIS intake throttle position at plot 814, and EGR valve position at 816. All plots are shown over time along the X-axis.

[0099] Vehicle propulsion may be started at t1. At the time of vehicle propulsion, the conditions for engine start may not be met, and the vehicle may be propelled by the torque of the electric motor alone. For example, the vehicle may be a hybrid vehicle operating in an electric mode. Between t1 and t2, as the driver's demand and, accordingly, the vehicle speed vary, the battery SOC may vary, with the battery SOC being reduced at a faster rate as the vehicle speed increases. As such, while the vehicle is propelled using the torque of the electric motor between t1 and t2, the piston temperature may be below a limit temperature 809.

[0100] To activate cylinder heating, thereby reducing particulate emissions and improving engine performance when the engine is subsequently operated, an intake compressor can be rotated while an upstream intake throttle is kept closed and an EGR valve is opened. Additionally, the engine can be positioned for increased blowthrough of warm compressed air. As the compressor rotates, the piston temperature gradually increases.

[0101] After t2, the driver's torque demand and vehicle speed decrease. As a result, the battery SOC may gradually decrease (at a slower rate) as only the compressor continues to rotate using battery power. Shortly after t2, a vehicle deceleration event occurs. During this event, instead of dissipating wheel torque as heat, the engine opportunistically rotates, without fuel, via the wheels. Based on the drop in wheel torque that occurs during the vehicle deceleration event, at least some of the wheel torque is applied to the engine rotation via a vehicle electric motor / generator, temporarily increasing the engine rotation speed. As the engine is slowly rotated via the electric motor, two effects occur. First, the piston temperature is further raised. Second, the fuel rail pressure is raised.As vehicle speed decreases, opportunistic engine operation is stopped. Fuel rail pressure can then gradually dissipate.

[0102] At t3, the vehicle speed increases again, but the conditions for engine restart are not met. Additionally, engine restart is undesirable because the piston temperature, while warmer than the piston temperature at t1, is still lower than threshold 809. Consequently, a large amount of particulate matter emissions can be generated if fuel is injected directly into the cold cylinder. Thus, engine restart is delayed, and the vehicle continues to be powered solely by the torque of the electric motor.

[0103] To further accelerate cylinder heating while the compressor is rotating, at t3 the engine can also be rotated without fuel at less than the engine crank speed. As such, the compressor and engine can be rotated via different electric motors, with the engine driven by the same electric motor that powers the vehicle, while the compressor is rotated via a dedicated electric motor. The engine can be rotated, for example, at 10-30 rpm. Rotating the engine slowly via the electric motor between t2 and t3 increases the piston temperature even further. In addition, the fuel rail pressure is increased and maintained at the elevated level.

[0104] Between t3 and t4, another vehicle deceleration event occurs. During this event, instead of dissipating wheel torque as heat, the engine opportunistically rotates faster, without fuel, via the wheels. Based on the drop in wheel torque that occurs during the vehicle deceleration event, at least a portion of the engine torque is applied to the engine rotation via the electric motor / generator, temporarily increasing the engine rotation speed (above the speed at which the engine was rotated at t2).

[0105] Between t4 and t5, due to the combined effect of compressor rotation and engine rotation, the piston temperature rises above the limit temperature 809. Thus, the engine cylinders can be considered ready for fuel supply when the restart conditions are met. In response to the increase in piston temperature, compressor rotation is deactivated, and the compressor slowly rotates to a stop. In addition, the EGR valve may be closed. At t5, the vehicle speed increases again, and the engine restart conditions are considered met. In particular, because the piston is sufficiently warm and further because the battery SOC is lower, engine restart is enabled. Accordingly, after t5, the engine is cranked faster via a starter motor, and fuel supply to the cylinder resumes.The engine speed then increases when the vehicle is driven with at least the engine torque. Additionally, the engine torque can be used to charge the battery. In response to the engine restart, the intake throttle is opened, and the opening is subsequently adjusted based on engine speed / load conditions.

[0106] It is understood that the example of Fig. 8 is a non-limiting example, and that further variations and combinations of compressor rotation, engine rotation, EGR valve position, throttle position, CRV position, intake heater operation, and valve timing based on heating demand may be possible.

[0107] In this way, a hybrid vehicle engine can be slowly cranked using an electric motor during a transition from operation in electric mode to motor mode to heat the engine prior to engine start. By slowly rotating the engine, without fuel, for a period prior to an imminent engine restart, heat generated from the air compressed in a cylinder during a compression stroke can be transferred to the cylinder walls and pistons and advantageously used to heat the engine. Alternatively, by rotating an intake compressor via its electric motor, heat rejected by the compressed air can be forced through the engine and used to heat the cylinders.By heating the cylinders with the intake throttle closed and the EGR valve open, the hot air can be pumped through the engine in a loop, improving heat transfer efficiency. By also opening a compressor return valve, the compressor energy can be used to heat a charge air cooler. By rotating both the engine and the compressor simultaneously, air charge heated by the compressor can be recirculated through the engine cylinders, and heat can be distributed to all engine cylinders, allowing for uniform cylinder heating. By warming the engine before an engine start, particulate emissions from the engine resulting from the directly injected fuel can be reduced, especially during a cold engine start. In addition, the fuel pressure can be sufficiently raised.The resulting improvement in the fuel injector's spray characteristics during restart further reduces particulate matter emissions from the engine. Overall, exhaust emissions during cold start and engine performance can be improved.

[0108] It should be noted that the example control and detection routines encompassed herein may be used with various configurations of engine and / or vehicle systems. The control methods and routines described herein may be stored as executable instructions in non-transitory memory. The particular routines described herein may represent one or more of a variety of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various illustrated actions, operations, and / or functions may be performed in the illustrated order, in parallel with one another, or in some cases, may be omitted.Likewise, the order of processing is not necessarily required to achieve the features and advantages of the exemplary embodiments described herein; rather, it is presented for illustration and description. One or more of the illustrated actions, operations, and / or functions may be performed repeatedly depending on the particular strategy being used. Further, the described actions, operations, and / or functions may graphically represent code to be programmed into the non-transitory memory of the computer-readable storage medium in the engine control system.

[0109] It should be understood that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, as numerous variations are possible. For example, the above technology may be applied to V-6, I-4, I-6, V-12, opposed-4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and / or characteristics disclosed herein.

[0110] The following claims point to certain combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims should be understood to encompass the inclusion of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by presenting new claims in this or a related application. Such claims, whether broader, narrower, the same, or different in scope with respect to the original claims, are deemed to be encompassed within the subject matter of the present disclosure.

Claims

[1] Procedure which includes: while a hybrid vehicle is driven by the torque of an electric motor (26), rotating an electrically operated intake compressor with an upstream closed intake throttle and an open EGR valve (152) until a piston temperature is above a limit value. [2] The method of claim 1, wherein rotating the electrically actuated compressor (114) comprises activating an electric motor (26) coupled to the compressor (114) and rotating the compressor (114) at less than a threshold speed. [3] The method of claim 1, further comprising operating an electric heater (121) coupled in an intake duct (142) during rotation. [4] The method of claim 1, wherein the EGR valve (152) is positioned in a low-pressure EGR passage (150) coupling an engine exhaust downstream of an exhaust catalyst to an engine intake upstream of the compressor (114), the method further comprising, during rotation, activating an electric heater (121) coupled to the exhaust catalyst. [5] The method of claim 2, further comprising, while rotating the compressor (114), rotating the engine without fuel via the torque of the electric motor. [6] The method of claim 5, wherein the electric motor (26) coupled to the compressor (114) is a first electric motor (26), and wherein driving the hybrid vehicle via the torque of the electric motor (26) comprises driving the vehicle using torque from a second electric motor (26). [7] The method of claim 6, wherein rotating the engine without fuel while rotating the compressor (114) comprises rotating the engine via the second electric motor (26) continuously at less than the engine crank speed. [8] The method of claim 6, wherein rotating the engine without fuel while rotating the compressor (114) comprises rotating the engine via the second electric motor (26) intermittently at less than the engine crank speed. [9] The method of claim 1, further comprising, during rotation, adjusting valve timing to increase positive valve overlap. [10] The method of claim 1, wherein said rotating occurs in response to a determined cylinder piston temperature being lower than said threshold. [11] The method of claim 1, further comprising, during rotation of the compressor (114), opening a compressor recirculation valve (172) coupled to the compressor (114) in a compressor bypass passage to increase recirculation through a charge air cooler (117) coupled downstream of the compressor (114). [12] The method of claim 1, further comprising, after the piston temperature is higher than the threshold, initiating fuel injection into the cylinder (30) to restart the engine. [13] Procedure which includes: while a hybrid vehicle is driven only by the torque of an electric motor (26), Rotating an engine without fuel via the torque of the electric motor (26) at less than one engine crank speed while operating an exhaust gas heater coupled to an exhaust catalyst and while maintaining an EGR valve (152) open and an upstream intake throttle closed to recirculate heated air charge through the engine. [14] The method of claim 13, wherein the rotating occurs in response to the temperature of the cylinder piston being lower than a threshold value, and wherein the rotating continues until the piston temperature is higher than the threshold value. [15] The method of claim 13, further comprising, during said rotating, operating an intake heater (118) coupled in an intake passage (142) of said engine. [16] The method of claim 13, further comprising operating an electrically actuated compressor (114) coupled to an intake of the engine while opening a compressor return valve (172) coupled to the compressor (114). [17] The method of claim 13, further comprising, during said rotating, adjusting cam timing to increase the positive overlap of the intake valve over the exhaust valve. [18] Hybrid vehicle method comprising: in response to a piston temperature being lower than a limit value, while the vehicle is driven only by the torque of the electric motor (26), during a first condition, rotating the engine without fuel via the torque of the electric motor (26) at less than the crank speed to heat all engine cylinders in turn as they undergo a compression stroke; and during a second condition, rotating an electrically actuated intake compressor with a compressor return valve (114) held open. [19] The method of claim 18, wherein during both the first and second conditions an intake throttle is kept closed and an EGR valve (152) is kept open, and wherein during both the first and second conditions spinning continues until the cylinder wall temperature is above the threshold, the threshold being based on the cylinder charge temperature. [20] The method of claim 19, further comprising, during any of the first and second conditions, operating one or more of an exhaust heater and an intake heater (118), wherein the exhaust heater is coupled to an exhaust catalyst positioned upstream of an EGR passage inlet, wherein the intake heater (118) is coupled to an intake passage (142) upstream of the compressor (114).

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